Despite the critical need to understand the processes and predictors behind adolescent substance use and risk behaviors, research has focused primarily on individual predictors rather than family dynamics, and mothers rather than fathers. Family systems theory would suggest that children are impacted both directly by parents' behavior (e.g., modeling risk behaviors) and indirectly by their parents' behaviors toward one another (e.g., coparenting) and their relationships with their parents (mother-child and father-child closeness). This article investigates links between parental substance use at child age 9 and children's substance use and delinquent behaviors at age 15, and relational mediators of these associations (coparenting, parent-child closeness). Data from 2,453 mothers, fathers, and children from the Fragile Families and Child Well-Being Study (Reichman et al., 2001) were analyzed. Fathers' drug and alcohol use at child age 9 were not directly associated with adolescent risk behaviors at age 15, but his drug use was associated with adolescent substance use indirectly via its influence on maternal coparenting and thereafter father-child closeness. Mothers' alcohol and drug use were both directly associated with later adolescent drug use and delinquency, and indirectly with delinquency via their associations with fathers' coparenting and thereafter mother-child closeness. Implications of the findings for intervention and prevention as well as future research are discussed.